[llvm] [LoopInterchange] Defer CacheCost calculation until needed (PR #146874)

[Ryotaro Kasuga via llvm-commits]

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@@ -407,6 +407,33 @@ class LoopInterchangeLegality {
   SmallVector<PHINode *, 8> InnerLoopInductions;
 };
 
+/// Manages information utilized by the profitability check for cache. The main
+/// purpose of this class is to delay the computation of CacheCost until it is
+/// actually needed.
+class LoopInterchangeCacheCostManager {
+  Loop *OutermostLoop;
+  LoopStandardAnalysisResults *AR;
+  DependenceInfo *DI;
+
+  /// CacheCost for \ref OutermostLoop. Once it is computed, it is cached. Note
+  /// that the result can be nullptr.
+  std::optional<std::unique_ptr<CacheCost>> CC;
+
+  /// Maps each loop to an index representing the optimal position within the
+  /// loop-nest, as determined by the cache cost analysis.
+  DenseMap<const Loop *, unsigned> CostMap;
+
+  void computeIfUnitinialized();
+
+public:
+  LoopInterchangeCacheCostManager(Loop *OutermostLoop,
+                                  LoopStandardAnalysisResults *AR,
+                                  DependenceInfo *DI)
+      : OutermostLoop(OutermostLoop), AR(AR), DI(DI) {}
+  std::unique_ptr<CacheCost> &getCacheCost();
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kasuga-fj wrote:

While I chose this to maintain the argument types of the other functions, I think returning a reference to unique_ptr is bad design. Should we change to return `CacheCost *` instead?


https://github.com/llvm/llvm-project/pull/146874